In the process for producing a semiconductor device such as IC and LSI, microfabrication by lithography using a photoresist composition has been conventionally performed. Recently, with the increase in integration of an integrated circuit, formation of an ultrafine pattern in the sub-micron or quarter-micron region is required. To cope with this requirement, the exposure wavelength also tends to become shorter, for example, from g line to i line or further to KrF excimer laser light. At present, other than the excimer laser light, development of lithography using an electron beam, an X-ray or EUV light is also proceeding.
Among others, electron beam lithography is positioned as a next-generation or next-next-generation pattern formation technology and a high-sensitivity and high-resolution positive resist is being demanded. In particular, for shortening the wafer processing time, it is a very important task to increase the sensitivity, but in the positive resist for electron beam, when high sensitivity is pursued, this causes a problem that the resolution is likely to lower.
In this way, high sensitivity is in a trade-off relationship with high resolution and further with good pattern profile, and it is very important how to satisfy all of these properties at the same time.
Also, in the lithography using an X-ray, EUV light or the like as well, it is an important task to satisfy all of high sensitivity, high resolution and good pattern profile at the same time.
In order to solve these problems, for example, in JP-A-2010-256419 (the term “JP-A” as used herein means an “unexamined published Japanese patent application”), JP-A-2000-29215 and JP-A-8-101507, a positive resist composition using a resin having an acetal-type protective group is disclosed, and it is stated that according to such a composition, the resolution, sensitivity and the like are improved.
In the positive image forming method, an isolated line or dot pattern can be successfully formed with this composition, but in the case of forming an isolated space or fine hole pattern, the pattern profile is liable to deteriorate.
In addition, a pattern forming method using an organic solvent-containing developer (organic developer) is also being developed recently. This method is supposed to enable stable formation of a high-definition fine pattern.
However, for forming a fine pattern with a narrow space width by using an organic solvent-containing developer, it is presently demanded to further improve the performance in terms of resolution, sensitivity and resolution in isolated space pattern formation.